1. Field of the Invention
The present invention relates to a test data analyzing method and system for use in estimation of a defect cause (defective process) of a product which is obtained through multi-step processes, such as, fabrication processes of integrated circuits, liquid crystal displays, optical transceivers, thin film magnetic heads, etc.
2. Description of the Related Art
Fabrication process of integrated circuits will be explained as an example. In general, fabrication process of integrated circuits is divided into initial process steps for forming plural chips on a silicon wafer and after process (or post process) steps for cutting individual chips, molding, and product finishing. Usually, in an electrical test that is performed at the last step of the initial process, a defective chip is found and only good quality chips proceed to the post process.
Particularly in the initial process, the ratio of good quality chips determined by the electrical test on every chip is called the percentage of good products, i.e., yield. Increasing this yield is very important in the initial process manufacture line especially for realizing low-cost production.
Many methods have been suggested to estimate defect cause(s) (defective process) aiming to increase yield. Among them is an analysis of the relation between a fabricating machine a product (wafer) passes through and test data. This method, as described in Japanese Patent Laid-open Publication (JP-A) Nos. 2000-12640 and H11-45919, analyzes a significant difference among plural fabricating machines used in the same process.
JP-A No. 2000-12640 discloses a method for analyzing, on the basis of ANOVA (Analysis of variance), the relation between fabricating machines a wafer passes through and a yield provided from an electrical test and for searching a process with a significant difference in the machines.
JP-A No. H11-45919 discloses a method for discovering a significant difference among fabricating machines by comparing coordinates of particles detected through a particle inspection which is carried out by each fabricating machine a wafer passes through. However, the above-described methods for discovering a significant difference among the fabricating machines are on the basis of an assumption that plural fabricating machines exist in one process.
To be short, JP-A Nos. 2000-12640 and H11-45919 provide a method for calculating a significant difference among fabricating machines. For this reason, in the case that a certain process uses one single fabricating machine for example, one cannot figure out a significant difference among fabricating machines for that process and the significant difference must be obtained outside of the estimated object of a defect cause (defective process).